Distillation and stabilization process



AP 23, 1940- D. G. BRANDT DISTILLATION AND STABILIZATION PROCESS Filed June 3, 1959 2 Sheets-Sheet 1 N xz. ZBOQ 23,99 23de HBAIBUEU L BNVdOHd 0.1. QNVdOUd und SNI INVENTOR DAVID G. B

DT mm% ATTORNEY April 23, 1940. D. G. BRANDT DISTILLATIONl AND STABILIZATION PROCESS Filed June 3, 1939 2 Sheets-Sheet 2 All NNN fm/Nrw,

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DAVID G B INVENTOR ATTORNEY Patented Apr. 23, 1940 PATENT oFFicE DISTILLATION ANDy STABILIZATION` PROCESS David G. Brandt, Westield, N. J., assigner to Power Patents Company, Hillside, N. J., a corporation of Maine Application June 3, 1939,` Serial No. 277,208

18 Claims.

'lhis invention relates to distillation and stabilization processesr for handling hydrocarbon mixtures. More particularly the invention relates y to` stabilization of `gasoline to eliminate undel (Yi sirable low boiling constituents and to produce a motor fuel product having a desired predetermined boiling range or vapor pressure.

This application is a continuation-in-part of the applicants pending applications Serial No. 548,062, led July 1st, 1931, and `Serial No. 195,- 681, led March 14th, 1938. The subject-matter disclosed and claimed in these applications will be referred to more in detail hereinafter in describing the apparatus shown in the drawings. Application Serial No. 195,681, was filed as a continuation-in-part of applications Serial Nos. 548,- 062; 624,979 and 720,539.

This application is also a continuation-in-p-art of the applicants prior pending application Serial No. 624,979, filed July 27, 1932, for improvements in Cracking of petroleum oil, now Patent No. 2,111,354, granted March 15th, 1938. This applicationdiscloses a process for condensing and stabilizing the hot vapors removed from a dephlegrnator of a cracking unit by passing all or a part of them in indirect heat exchange with a body of condensate in the bottom of a stabilizer to heat and vaporize condensate ofthe body,

`after which all of the vapors are passed through a heat exchanger and a condenser to cool and condense the gasoline constituents and certain of the lower boiling hydracarbons. The condensate and uncondensed gases are conducted to a receiver in which the condensate is separated from uncondensed gases and from which it is pumped in indirect heat exchange with the vapors in theheat exchanger to heat it, after which it is introduced into the mid-portion of the stabilizing tower. A pressure of from 250 to 300 pounds per square inchyderived from the cracking unit proper, is disclosed as being maintained in the condensate receiver. Provision is made for condensing overhead vapors from the stabilizer and returning a portionof the resulting condensate to the upper part of the stabilizer as a reiiuxing medium to maintain the desired temperature at the top'of the stabilizer tower. The present application is also a continuationin-part of applicants pending application Serial No. 720,539, filed April 14th, 1934, for improve- `ments in Method of processing crude petroleum. This pending application discloses a process in which the stream `of the pressure distillate vapors produced in the cracking operation disclosed therein, is passed from a high pressure dephlegmator at a pressure of from 100 to l250 pounds per square inch, and all or a portion thereof passed in indirect heat exchange with a body of liquid gasoline in the bottom of a rst stabilizer tower section to heat the gasoline. Subsequently all or a portion of the whole vapor stream from the high pressure dephlegrnator is passed in indirect heat exchange with a body of liquid gasoline in the bottom of a second stabilizer tower section to heat this second body of gasoline, after which all of the constituents removed fromthe high pressure tower are conducted through a heat `exchanger and a condenser to cooland condensethe gasoline constituents and certain of the lower boiling hydrocarbons contained in the vapors. The resulting condensate and uncondensed gases are conducted into a receiver from which the uncondensed, relatively dry gases are removed from a line provided with an automatic pressure controlled release valve.

In accordance with this 1934 applicatiomthe condensate collected in the receiver is conducted through a float valve controlled line and passed in indirect heat exchange with the vapors in the heat exchanger in order to heat the condensate, after which it is introduced into the mid-portion of the first stabilizer tower section. The pressure distillate introduced into the rst stabilizer section is rectied under conditions` adapted to removethe low boiling point constituents such as propane and a part of the butane as vapors, which are subjected to `condensation to produce an overhead condensate which is used as overhead reiiux to control the temperature at the top of the stabilizer tower section. The gas remaining uncondensed from this overhead condensingoperation is removed from a separatorreceiver through an automatic pressure regulated relief line. The stabilizer gasoline recovered in the bottom of the first stabilizer tower section is conducted at lowerpressure into the mid-portion cf the second stabilizer tower section wherein the light gasoline constituents are vaporized and separated from the heavier portions of the gasoline by fractionation. The light gasoline constituents are removed as vapors from the second stabilizer tower section through a pressure controlled vapor line, condensed and collected in a receiver. Portions of this light gasoline condensate are pumped respectively, into the upper part of the second stabilizer tower section to control the top temperature therein, and into the upper mid-portion of the rst stabilizer tower section above` the point of introduction of the pressure distillate, to aid in controlling the fractionation therein. The heavy gasoline collected in the bottom of the second stabilizer tower section is removed through a float valve controlled line, cooled and refined separate from the light gasoline fraction taken overhead from the second stabilizer section. This pending application discloses the condensation of the pressure distillate and the fractionation thereof in the stabilizer tower sections at pressures of from 100 to 250 pounds per square inch which are derived from the pressures in the` cracking unit proper. The use of these pressures aids in the condensation of lower boiling constituents such as propane and butane along with the pressure distillate, and also aids in the fractionation in the first stabilizer tower section.

The primary object of the present invention is the provision of an improved process for recovering and condensing mixtures of hydrocarbon vapors such as pressure distillates, natural and straight run gasolines, desirable hydrocarbon gases, and the stabilization of the resulting condensates or mixtures under conditions adapted to separate lower boiling point constituentsand provide products of predetermined boiling range. The process of the present invention is in certain respects an improvement over certain features of the process of the Behimer Patent No. 1,874,860.

In general, the present invention relates to the production of rectified products such as stabilized gasolines or motor fuel having a predetermined vapor pressure or boiling range from materials such as those described above. In accordance with one form of the invention, the steps of the improved process include the passage of the hydrocarbon mixture to be treated in vapor or gaseous form through a heat exchange zone in indirect heat exchange with a condensate produced in the process, the substantially complete condensation of the readily condensable constituents under a relatively high pressure so that substantially only the relatively dry gases remain uncondensed, the collection of the resulting condensate and its separation from the uncondensed gases, the passage of the collected condensate through the heat exchange zone referred to, and the introduction of the resulting heated condensate into a fractionating or stabilizing column wherein the condensate is rectified to remove overhead undesired volatile constituents.

In the modified form of the improved process the steps include the cooling and condensation of the vapor mixture being treated to produce a condensate which is subjected to rectication in a stabilizer tower. In this condensation operation the cooling and condensation is effected by passing the vapors or a portion thereof in indirect heat exchange with the rectified product in the base of the stabilizer tower, then through a heat exchanger and a condenser. The condensate resulting from these cooling steps, or a portion thereof, is conducted in indirect heat exchange with the vapors in the heat exchanger, mixed with another portion thereof (if any) not passed through the heat exchanger, and the total mixture conducted into the stabilizing tower.

The present invention also involves other features including certain automatic control steps which have been found to materially aid in carrying out the process. Those skilled in the art will also appreciate the presence of additional advantages and features from a consideration of the following more detailed description of the invention taken in connection 'with the accompanying drawings in which:

Fig. 1 illustrates somewhat diagrammatically an apparatus adapted for carrying out one form of the improved process of the present invention. The apparatus shown in Fig. 1 is the same as that shown and describedy in applicants application Serial No. 548,062.

Fig. 2 is a more or less diagrammatic vertical view showing arrangement of apparatus elements particularly adapted for carrying out a modified form of the improved process of the present invention. The apparatus as shown in this figure is the same as that shown and described in applicants pending application Serial No. 195,681.

In Fig. 1 of the drawings (as described in application Serial No. 548,062), conduit I is a line for conducting vapors and xed gases from a cracking still dephlegmator into one of a series of heat exchangers I2, I4. I6 for the mixed condensate and gas connects the heat exchanger I4 with a final cooler I8 for the condensate and gas. A valved conduit I5 also connects line I0 directly with the cooler through line I6. A valved conduit 20 conducts the condensate and gas from the cooler I8 to a receiver 22. Any fixed gas separating from the condensate in the receiver 22 is conducted through a conduit 24 to a fuel gas header 25 having a valve 21 and passed to storage.

The receiver 22 is also in valve-controlled communication with a flow tank 26 through the valved conduits 24 and 28. A conduit 30 having therein a pump 3| conducts liquid under pressure from the flow tank 26 through the preheaters I4 and I2 in series, and thence through a valvecontrolled conduit 32 into the vertical mid-portion of a fractionating column 34 of Well-known construction. Connected with the lower `portion of the column 34 is an indirect heater or reboiler 36 adapted to maintain the liquid in the bottom of column 34 at a predetermined raised temperature.

A vapor line 38 leads from the top of the column 34 to a condenser and cooler 40. Liquids condensed in the condenser 40 flow therefrom through valved-controlled line 42, and may be conducted in whole or in part into the upper portion of the column 34 through the valvedcontrolled lines 44 and 46 by means of a reiiux pump 48. A mid-portion of the condenser 40 is connected through a valved conduit 50 with the fuel gas header 25 in the manner shown.

A valve-controlled linev 52 connects the reboiler 36 with the mid-portion of a second fractionating column 54 and serves for conducting partially stabilized distillate from the column 34 to column 54. Column 54 has associated with its lower portion a reboiler 56 adapted, like reboiler 36, to be heated by high pressure steam and having connections 58 and 60 for recycling the reheated liquid to the bottom of the column 54.

A vapor line 62, having therein a pressure relief valve 64, connects the top of the column 54 with a condenser 66. Condensate from 66 ows to a propane receiver 68 through a line 10, while fixed gases flow from the said condenser 66 through the valve-controlled line 12. The fixed gases from condenser 66 and receiver 68 pass to the fuel gas A valved outlet line and 94.

The propane receiver 58 is connected `with the upper portion of the column 34 by means of the valve-controlled conduits 'I4 and 16, branch conduits 1B, and cycle-pump 80.

with the upper portion of the column 54 through the conduit 14, reflux pump 82 and valvescontrolled conduit 84. The said receiver 68 is also in controlled communication through conduit 74, storagepump 85 and valved conduit 88 with a propane cooler 80 and thence through line9| with propane storage vessels 92. Propane from line 88 may be passed directly to line 'I0 by a valved connecting line 89.`

A valved conduit Slconnects the reboiler 5 with the midportion of a third fractionating col-- umn 88. A reboiler is connected with the lower portion of the stabilizing column 98, through the conduits |02 and |04, and serves for heating the body'oi` partially stabilized distillate maintained in the bottom of that column.` `A vapor line |06, having therein a` pressure relief valve |08, connects the topof the stabilizing column 88 with a condenser I|0. An outlet line ||2 leads from the condenser to a butane receiver |I4.

The butane receiver is in controlled communication with the upper mid-portion of the frac# tionating column 54 through the valved lines I6, |53, cycle-pump I 20, line |22 and the valve-oontrolled branch lines"|24. Similarly, the butane receiveris in controlled communication with the upper portion of the fractionating column 38 by means of the conduits IIB, |30, reiiux pump |32, and valved conduit |34. The receiver II4 is also in communication with butane storage tanks |35 through the lines I I6, I 35, storage pump |38, line |40, cooler |42 and line |44. Butane from line |43 may be passed directly to line IIZ by a valved connecting line |4| A` conduit |62 leads from the reboiler |30 to a cooler |64, from thence the cooled and stabilized distillate is conducted through valved conduit |80 to a stabilized distillate treating plant (not i shown).

For use in recovering propane and butane from f heat contained `therein is utilized for heating un-` gas line |58 having therein a compressor pump I5@ `leads to the lower portion of the absorber I5!! from the gasoline run-downtanks or `from a source of rich gases in the crude still receiving house. l y

In the practice of the invention in connection with the stabilization of` pressure distillates from a hydrocarbon cracking operation in the apparatus of ligure l.,` the vapors and xed gases from a cracking still dephlegmator `ow successively through line lll,` and heat exchangers I2 and I4, in each of which aconsiderable` portion of the stabilized distillate flowing to the first fraction,-

` ating column 34. The resultant condensate and gas iiow from heat exchanger I4 into the final cooler i8 where they are cooled to approximately '70 F., and in which considerable additional portions `of the vapors are condensed. The mixed condensate, vapors and gases then flow into receiver 22. i

I Similarly the propane receiver 88 is in controlled communication` than the cracking still-operating pressure.

`thus carried away with these fixed gases.

I'he heat exchangers I2 and I,4,`cooler I 8, and the receiver 22 are maintained at substantially the cracking still-operating pressure,i. e`. for example, approximately 235 lbs. per square inch, gauge, in order vto condense all constituents condensable under these conditions and leave a substantially dry gas. The "dry or fixed gases iiow from ythe receiver 22 through valved conduit 23 and conduit 24 to the fuel gas header 25 past the pressure relief valve 21.

The distillate collected in the receiver is forced through line |52 into the top of absorber tower Iiili where it flows downwardly countercurrent to a flow of rich gases being pumped into the lower portion of the absorber through line |58 from the crude still receiving house or from gaso-l line run down tanks. late then flows to tank 26 through conduit |56.

This distillate in the iiow tank 26 contains all of the pentane and heavier components of the cracking still vapors and `considerably more propane and butane than could be condensed from the latter at low pressures or pressures below the `cracking still pressure, together with additional propane andbutane recovered from the gases of the gathering system.

The enriched pressure distillate is then introduced into the mid-portion of the first column- 34 under a pressure very substantially greater This is accomplished by means of the pump 3| which forces the unstabilized distillate from the ow tank 23 under high pressure in series through preheaters I4 and I2, and through line 32 to the column 34.

Where the maximum `propane recovery is desired, a pressure of approximately 400 lbs. per square inch, absolute, at the top of column 34 is employed. The pressure at which this column is operated will be determined by the percent of propane that it is desired'to recover. The quantity of propane necessarily released with the methane and ethane from the rst column of the stabilizing unit through line 38 decreases with increased column pressure. Since the 'loss of propane is undesirable, the column 34 is necessarily operated at higher pressures than are usual in stabilizer operation. Y

v The vapors and gases froml the first fractionating column flow through line-'i8 to the condenser 43 where portions of the vapors are `condensed; and all or `a selected portion of such condensatefis returned as refluxto the upper part of the said column through the line 46.

' The methane and ethane, together with the small amount of propane in equilibrium` therewith at the temperatures and pressure existing in condenser 49, are released as gas from. the latter and pass into the `fuel gas header 25. The conditions in the condenser are maintained such as to `keep at a minimum the per cent of propane These gases contain about 16% by volume of propane under the conditions of operations named, the balance of the gas being methane andv ethane.

Pressures in the column 34 and condenser 40 can be maintained quite constant by proper adjustment of the valves in conduits 42 and 50, because of the relatively large proportion of xed gases in the vapors flowing from column 34.

The pressure distillate at the bottom of column 34 is preferably maintained at a temperature not exceeding 300 F. `The condensate refluxed through line 45 is in amounts and at atemperature adapted `to maintain `a normal operating The thus-enriched distilytemperature of around 70 F. in the upper portion of the column 34. Inl addition to the heat supplied vto the unstabilized distillate by 'the heat exchangers l2 and 14, the reboiler 36 is employed to supply heat required for maintaining the `desired bottomv of column operating temperature Propane recycled from the second fractionating column 54 in a manner subsequently to be described preferably isl employed to assist in developing the necessary vapor pressure `at the bottom of column S4 at `the maximum operating temperature, which is preferably of 300' F. or

less.

The partially-stabilized pressure distillate or liquid in the base of column 34, free from methane and ethane, is then transferred to the midportion of the fractionating column 54, vWhere ample, a pressure of approximately 210 lbs. per

square inch, absolute, and a top-of-column temperature of 110 F. is satisfactory. The bottomof-column temperature preferably shouldf not exceed 300F. A partial 4evaporation will result,

upon the reduction of the pressure on the distillate from that of the first column lto that of the vlower portion Vof the second column.

The reboiler 56 supplies additional heat thus made necessary by revaporization at the base of the column 54 caused by this reduction of pres-- sure. In this way, the desired temperature and reflux ratio can be maintained in the column.

The pressure reducing valve 54 in the vapor line' 52 leading from the second column facilitates the maintenance of a uniform temperature and pressure in this column, and makes possible the condensation of the vapors from the column 54 at a lower pressurev than that in the column, so

Thepartially-stabilized. pressure distillate or l hydrocarbon mixture is conducted from the reboiler 55 into the lower mid-portion of the thirdV fractionatingcolumn 98, the latter preferably being maintained Vat an operating pressure of approximately 60 lbs. per square inch absolute, andpreferably having a bottom-of-column ternperature of around 250 Ffand a top-of-column Vtemperature of around 1l0 F.

While the above-mentioned temperatures and pressure conditions may be satisfactorily employed in the process, it will be understood that the conditions of operation of the various co1- covered in the' receiver H4; while decreasing thev column pressure and increasing the. reboiling at the base of the column will 'decrease the vapor pressure of the stabilized product and increase the butane yield. Byincreasing the pressure in the column 98 to 70 lbs. per square inch, a propane-free distillate having a vapor pressure of about 9 lbs. per square inch can be produced. The'pressure-reducing valve |08 makes possible the maintenance of uniform conditions in the top of the column 98.

It is Well known that considerable polymerizaj tion occurs when pressure distillate vor gasoline is heated to high temperatures in accordance with the practice ofthe .prior art. Such polymerization -is avoided or substantially reduced `in the firstv fractionating column 34 by reuxing condensate from-condenser 40, and by recycling propane thereto `from the second column` receiver 68; thus increasing the vapor pressure of propane in the Aboiling distillate at the base of the rst column and preventing a temperature rise above Similarly polymerization of the pressureV distillate Within the second column is prevented or,

substantially reduced byj recyclingbutane from the third column receiver H4 and by refluxing propane drawn` from receiver 68. Thus the temperatures at the base of the firstand'second columns are prevented from substantially exceeding 300 F. kThe temperature at the base of the third column will always be under 300 F., regardless of operating procedure, because of the very materially lower column pressure. In order` to strip valuable components from gas gatheringsystems and from a crude still receiving house orgasoline down-run tanks, and to reducelthe propane and butane cycle loss in the fractionating columns 34 and` 54, rich gases from gathering systems are compressed and are passed into theabsorber Vl 50 in intimate counter- Currentcontact with condensed unstabilized pressure distillate` or wild gasoline, prior to pumping-the same under pressure into the fractionatingcolumn 34. V:Only such gases as can be collected with minimum air dilution (from air being drawn intotanks and lines) are suitable for this purpose. The gathered gases can not only be stripped ofthe pentane and heavier components, but also of a good portion of their propane and butane as well, under suitable pressure and temperature conditions.

The three-column'stabili'zing plant shown in Figure 1 is a exible unit, and its operation as hereinbefore described canbe controlled to produce at will, maximum or minimum yields of propane and butane and to -vary the vapor pressure of the pressure distillate or gasoline asI desired for the purposeof meeting seasonal re- -densers adapted to return a selected part of the 75 e ating tower or `dephlegrnator 202 through a valve condensate therefrom by gravity to the top of the respective fractionating columns, proportional amounts of the condensate being conducted away to storage in suitable manner.

. In` processing crude petroleum oil in the apparatus shown in Fig. l, a number of fractionating stages may be used so that gasoline, kerosene, furnace oil, light lubricating stock and heavy lubricating stock may be successively removed overhead at diminishing pressures through the` stages. The last stages of. distillation may, if desired, be conducted under subatrnospheric pressure.` In many instances it may not be desirable to enrich the condensate in the receiver 22 with gases from a gathering system. In such instances the condensate is conducted from the receiver 22 through the valved lines 24 and 28 direct to the flow tank 26.

i Referring to Fig.`2 of the 'drawings (as described in application Serial No. 195,681), the vapors to bei handled `in the apparatus shown therein are conducted overhead from a fractioncontrolled vapor line 204. The tower 202 may comprise the usual high pressure tower of a cracking unit in which a pressure of approxi mately 250 lbs. per square' inch is maintained, or it may comprise the fractionating tower used for the fractionating of crude oil in which the gasoline hydrocarbons are separated out and retially dry i moved overhead as vapors along with lower boiling hydrocarbons. In almost every conversion `prficess where hydrocarbonsr are converted into gasolinev motor fuel, a fractionating tower such l as the tower 202 is employed `for separating the pressure gasoline constituentsvfrom higher boiling hydrocarbons. Inv practically all of these operations the fractionationin the tower 202 is controlled so that the overhead vapor `fraction `will have the desiredend boiling point.

`Assuming for example that a pressure of approximately 250 lbs. per square inch is maintained in the tower 202 from .iaihydrocarbon `conversion operation, the vapors `at approximately this pressure are .conducted through the line 204 and all or a portion thereof passed by means of a line 206through an indirect `heat exchanger 208 mounted in the base` of a1 stabilizer column 2m: The vapors from the `heat exchanger 208 are passed by means` of a line 212 through a heatexchanger 2|4, and a water cooler-condenser 2l6 to condense all ofthe gasoline constit- `uentsland certain of theun'desired lower boil- The use of high pressure in the cooling and condensing elements of the apparatus, and in the receiver 220 permits the condensation of, practically all of the desired hydrocarbons as "well as some undesirable constituents, so that the gases separated out in the receiver are substan- 'Ihese gases are removed from the separator 2,20 through aline 222 which is provided with an automatic pressure controlled' valve,V operated by the pressure in the receiver 220 to maintain a desired maximum back pressure. A portion of the condensate collected in the receiver 220 is preferably recycled in accordance with the `usual practice as a refluxing medium to control the temperature in the top of thetower 202, the end point of the product,`

and maintain a desired reilux ratio in the tower. Accordingly, condensate is withdrawn from ythe receiver 22d through a line 224 and forced by means ci a pump 22E through` a line 228 into the topiof the tower `202. The quantity of condensate thus introduced into the tower 202 as reux is controlled by the pump 226 whichacts by well# known means in` response to a flow controller or to the variations in temperature in the top oi the tower 2(42, as transmitted for example from a tnermocouplc 230, through the connecting leads 232. i l

The condensate produced in the above operation (that used as reflux in tower 202 is merely recycled and not deducted from the production) is withdrawnfrom the receiver `220 through a i line 224` (whichconnects intothe line 224), by means of an automatically controlled pump 236 and passed through a line 238 from which a portion or all, of this condensate is conducted through a valved line 240 and then in indirect heat exchange with the vapors passing through the heat exchanger 2I4. e

The flow of pressure distillate to the tower 2I0 `may be controlled, as shown, by the iioat valve mechanism, or by a iiow controller. Preferably the pressure distillate is supplied to the tower 2 I0 at a substantially constant rate and the oat used only Aas a high and low level alarm.

The preheated c-ondensate from the exchanger 2id is conducted through lines 242 and 244 into the mid-portion of the stabilizer tower 2| 0 i'or rectiiication. In carrying out this step of the process the proportion of condensate passed through the line. 240 and heat exchanger 2|4 is preferably` automatically controlled in accordance with the temperaturek at which the condensate enters the tower 210.` 'I'his entrance temperature as well as the point of introduction of the pressure distillate into the tower 2|0 is selected to correspond with the desired temperature gradient of the tower. Therefore the temperature of the condensate entering the midportion of the tower 2 I 0 is controlled from a thermocouple 246`mounted in theY line 244. This thermocouple is interconnected, by means of a connection 248, with an automatic control valve mounted in a bypass line 250 `between the lines 238 and 244. The thermocouple 246,r after be-l ing setto control and-maintain the entrance temperature of the pressure distillate, controls the valve in the bypass 250 to regulate the amount of condensate i heated in the heat exchanger 2M.

The bottom temperature in the stabilizer tower 2| 0 is preferably controlled automatically to supply the necessary heat by regulating the heating ofthe body of condensate inthis tower by vapors from the line 204. This may be accomplished automatically in accordance with responses from a thermocouple 252 mounted in afbody of liquid 4in the tower 2I0, the thermocouple being connected with a control valve mountedin a bypass line 254 between lines 204 and 2 l2. The thermocouple `252 is set to maintain `a predetermined temperature so that a slight drop in the temperature of the body of liquid in the bottom of the tower 2| 0 will cause the thermocouple to automaticallycloseth'e valve in the bypass line 254ltoincrease the proportion of hot vapors passed through the tubes of heat exchanger 288. On the other hand a slight rise in temperature in the bottom-'of the tower 210 above the predetermined point will cause thermocouple' 252 to open the. valve inthebypa'ss 254. -The lines 212 and 240 near the bypasses 4250 and 254 are preferably valvedin order to` provide a slight pressure drop in these lines, so that the automatic control will` be completely effective.

' The. pressure distillate or other unstabilized 'gasolinebor motor fueli material introduced into the mid-portion of the tower 218 isrectiiled to remove overhead the undesirable constituents which in the case of `gasoline would 4usuallyinclude all of the propane and similar, and lower boiling constituents, as well as apart of the butane fraction. The undesirable hydrocarbons are discharged overhead y.from vthe tower 218 Y.in vapor form through aline 256, a portion thereof condensed by condenser 258, and the resulting products conducted through av line 260 into a vapor-liquid separator 262.'` lUncondensed gases are removed "from this` separator through an automatic pressure valvecontrolled line 264. A portion of the condensate collectedninv receiver 262 is preferably used as reiiux in the topof the tower 218 in order to controlthe temperature therein and the initial point of the nally desired product. This condensate is withdrawn through a line 266 and forcedby meansof a pump 268 and a line 210 into the" top ofthe tower 2li). The amount of this condensate introduced intothe tower 2li() is controlled tc. provide the desired reiiux ratio by a iiow controller, or'by a thermocouple 212 which regulates the speed of pump 268 through a connection 214; Any excess condensate collected in the receiver2ii2 is.w ithdrawn through a `iioat valve controlled line 216. l y f'gThestabilized product produced in the tower 2 I `is withdrawn from the bottom thereof through ailoatvalve controlled line 218. A `high superatmospheric pressure is preferably maintained in the fractionatingtower 2li), preferablyjsubst'antially exceeding the pressure inthe receiver. 220.. For example, in the stabilization of pressure distillates, a pressure of from 300 to 350 pounds yper square inch is preferably employed in this tower. Where the process is used for.I the stabilization of vapors derived from low pressure` .operationsythe pressure in the receiver 220 may be` approximately atmospheric, but regardless: ofthis pressure the stabilizer tower 210 is preferably operated at a high superatmospheric pressure which is .derived from the pump 236. Extensive commercial operations have shown unusual advantages in carrying out the rectification in the tower 216 vat pressures higher. than that in the separator 220 orthe iractionating tower 202. In stabilizing a pressure distillate at a pressure of 300 lbs. in the tower 2 I0 to produce a product having a Ried vapor pressure of nine pounds per square inch, it was necessary to maintain a bottom temperature in the towerof'approximately 350 F. and a top temperature of about .135 F. The invention'is obviously not limitedto the treatment of distillates` obtained inrthejpressure cracking of petroleum, but may beapplied to the treatment of various hydrocarbon mixtures such as wild gasoline, natural gas,and coal tai1 vapors for the purpose of producing a liquid hydrocarbon mixture of preselected vapor .pressure and for the recovery ofpropane' andbutanelt is to be `understood that .theterms f-fpropane. and

fbutanel asused in this specification and the accompanyingclaims include other hydrocarbons of similarboiling point. It is apparent that in the handling of vapors and gases from `acraclring unit, that.' thepropane and. butane fractions l willinclude olens of:similar'. boiling point to propane and butane.

.Tlflsapplication contains theclaims from application Serial No. '548,062 as allowed, .and the claims fromv application Serial No. 195,681 held in eiect to be indivisible from certain claimsof application Serial No. 584,062.. .Certain ofthe subject-matter ydisclosed in .the latter application, and originally claimed'therein, is claimed in divisional application Serial No..104,387, led October '7th, 1936, issued as Patent No. 2,168,316 on August 8, l1939.

Having thus described the ginvention, what is claimed as newis: i

The method of stabilizing hot vapors,.which l0:

comprises partially cooling said hot vapors in a rst cooling zone to eiect condensation and separation of substantially all ,ofI the constituents heavier Ithan those desired inthe `final distillate product, removing. the `remaining vapors. and passing them first in indirectheat exchange with a distillate stock, topartially condense said vapors and heatsaid` distillate stock, then in indirect heat exchange .with another cooling medium to cause the iinal desired degreeof condensation of the vapors, whereby substantially'all .of the constituents thereofA desired in theiinal product are'v condensed, with some undesired constituents, collectingresulting condensate and removing incondensible lgases therefrom,vpass ing condensate so obtained` in indirect heat exchange with said hot vapors, assaid distillate stock, whereby said hot vapors are `initially cooledand `said condensate is heated, introducing resulting heated condensate into an intermediate point in a stabilizing column under, substantially superatmospheric pressure wherein, undesired excessively volatile constituents areseparated as vapors from said desiredv constituents'as liquids, removing said undesired excessiVQlY volatile constituents from the top of said- 'V column, withdrawing the stabilized product yfrom the baseofsaid column and applying additional heat from an externalsource to the base of said column. y y y 2, The process of fractionating hot vapors removed from a distilling operationjwhich comprises passing them `first in indirect heat exchange with a distillate" stock to partiallycondense said vapors and heat said distillate stock, then in indirect heat exchange with `another cooling medium to cause. the nal Idesired degreev of condensation of the vapors whereby substantially `all ofthe constituents thereof ldesired in the iinal f product are condensed withwsome constituents undesired in they iinalproduct, collecting `the resulting condensate and` removing any `uncon` densibley gases therefrom, passing. condensate so @meinte in .indireat heet .exhaneewith Said hot vapors'. as lsaid distillate stock ,whereby `said ,hot

vapors ar initiallycooled andlsaid condensate is 05` are removed in 'vapor form Afro-m a high temperature dephlegmator, condensed, and the resulting condensate then stabilized in a fractionating tower, the improvement which comprises passing vapors removed from said dephlegn'iator in indirect heat exchange with a body of liquid gasoline material in the base of said tower, the vapors passed in said heat exchange being sucient to maintain the desired temperature at the base of said tower, passing all of the vapors removed from said dephlegmator including those i passed in said heat `exchange through a heat exchanger and a condenser to cool the vapors and condense the gasoline constituents and some of said lower boiling hydrocarbons, separating the resulting condensate from the uncondenseol hydrocarbons in a separating zone, passing resulting condensate from said separating zone at a pressure higher than that maintained in said separating zone into the mid-portion of said fractionating tower, conducting a sufficient portion of the condensate passed to said tower in indirect heat exchange with vapors in said heat exchanger to bring the entire condensate passed to the mid-portion of said tower to a predetermined desired temperature, and stabilizing the condensate introduced to said tower to eliminate therefrom undesired low boiling point constituents.

13'. The process of stabilizing gasoline as dened by claim 12 in which the quantity of vapors passed in indirect heat exchange with the body of gasoline in the bottom of said tower is automatically controlled in accordance with the temperature of said body.

14 rfhe process of stabilizing gasoline as dened by claim 12 in which the condensate passed from said separating zone through said heat exchanger prior to its introduction into the midportion of said tower, and in which the quantity of condensate passed through said heat exchanger is controlled in accordance with the 'temperature of said mixture prior to its introduction into the mid-portion of said tower.

zone, passing separated condensate from said zone in indirect heat exchange with the vapors passing through said heat exchanger to heat the condensate to a predetermined temperature and then introducing the resulting heated condensate into the mid-.portion of said fractionating tower, and rectifying thev condensate introduced into said tower to stabilize the same and eliminate undesirable low boiling point hydrocarbons.

16. In the production of a rectied product having a predetermined boiling range from a vapor mixture containing `the constituents of said product and lower boiling point constituents, in which the vapor mixture is condensed and the resulting condensate -fractionated under rectifying conditions in a fractionating tower, the improvement which comprises passing the vapor mixture at a` relatively high temperature in indirect heat exchangeI with a body of rectified product in the bottom of said fractionating tower to maintain the desired temperature therein,y thereafter passing the lvapors through a cooling zone to furthercoolV the vapors and condense the constituents of said product as well as some of said lower boiling point constituents, separating the resulting condensate from any uncondensed vapors in a separating zone, passing separated condensate from said separating zone in indirect heat exchange with the vapors passing through said cooling zone to heat the condensate to a predetermined temperature and then passing the resulting heated condensate into the midportion of said fractionating tower, and rectifying the condensate introduced into said tower to produce said rectied product having said predetermined boiling range and eliminate constituents of lower boiling point.

17. The process defined by claim 16 in which said vapors are' condensed at a substantially high superatmospheric pressure land in which said rectication is carried out at a pressure higher than that used in said condensation.

18. The process defined by claim 16 in which the temperature of'the condensate introduced into the mid-portion of 'said fractionating tower is controlled by regulating the proportion of said condensate passed through said cooling zone and heated by the indirect heat exchange withl hot vapors passed therethrough.

DAVID G; BRANDT. 

